mainline/master boot bisection: v4.15-rc3 on peach-pi #3228-staging
Daniel Vetter
daniel.vetter at ffwll.ch
Mon Dec 11 09:05:52 PST 2017
On Mon, Dec 11, 2017 at 11:30 AM, Guillaume Tucker
<guillaume.tucker at collabora.com> wrote:
> Hi Daniel,
>
> Please see below, I've had several bisection results pointing at
> that commit over the week-end on mainline but also on linux-next
> and net-next. While the peach-pi is a bit flaky at the moment
> and is likely to have more than one issue, it does seem like this
> commit is causing some well reproducible kernel hang.
>
> Here's a re-run with v4.15-rc3 showing the issue:
>
> https://lava.collabora.co.uk/scheduler/job/1018478
>
> and here's another one with the change mentioned below reverted:
>
> https://lava.collabora.co.uk/scheduler/job/1018479
>
> They both show a warning about "unbalanced disables for lcd_vdd",
> I don't know if this is related as I haven't investigated any
> further. It does appear to reliably hang with v4.15-rc3 and
> boot most of the time with the commit reverted though.
>
> The automated kernelci.org bisection is still an experimental
> tool and it may well be a false positive, so please take this
> result with a pinch of salt...
The patch just very minimal moves the connector cleanup around (so
timing change), but except when you unload a driver (or maybe that
funny EPROBE_DEFER stuff) it shouldn't matter. So if you don't have
more info than "seems to hang a bit more" I have no idea what's wrong.
The patch itself should work, at least it survived quite some serious
testing we do on everything.
-Daniel
> Hope this helps!
>
> Best wishes,
> Guillaume
>
>
> -------- Forwarded Message --------
> Subject: mainline/master boot bisection: v4.15-rc3 on peach-pi #3228-staging
> Date: Mon, 11 Dec 2017 08:25:55 +0000 (UTC)
> From: kernelci.org bot <bot at kernelci.org>
> To: guillaume.tucker at collabora.com
>
> Bisection result for mainline/master (v4.15-rc3) on peach-pi
>
> Good known revision:
>
> c6b3e96 Merge branch 'for-linus' of
> git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux
>
> Bad known revision:
>
> 50c4c4e Linux 4.15-rc3
>
> Extra parameters:
>
> Tree: mainline
> Branch: master
> Target: peach-pi
> Lab: lab-collabora
> Defconfig: exynos_defconfig
> Plan: boot
>
>
> Breaking commit found:
>
> -------------------------------------------------------------------------------
> commit a703c55004e1c5076d57e43771b3e11117796ea0
> Author: Daniel Vetter <daniel.vetter at ffwll.ch>
> Date: Mon Dec 4 21:48:18 2017 +0100
>
> drm: safely free connectors from connector_iter
> In
> commit 613051dac40da1751ab269572766d3348d45a197
> Author: Daniel Vetter <daniel.vetter at ffwll.ch>
> Date: Wed Dec 14 00:08:06 2016 +0100
> drm: locking&new iterators for connector_list
> we've went to extreme lengths to make sure connector iterations
> works
> in any context, without introducing any additional locking context.
> This worked, except for a small fumble in the implementation:
> When we actually race with a concurrent connector unplug event, and
> our temporary connector reference turns out to be the final one, then
> everything breaks: We call the connector release function from
> whatever context we happen to be in, which can be an irq/atomic
> context. And connector freeing grabs all kinds of locks and stuff.
> Fix this by creating a specially safe put function for
> connetor_iter,
> which (in this rare case) punts the cleanup to a worker.
> Reported-by: Ben Widawsky <ben at bwidawsk.net>
> Cc: Ben Widawsky <ben at bwidawsk.net>
> Fixes: 613051dac40d ("drm: locking&new iterators for connector_list")
> Cc: Dave Airlie <airlied at gmail.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Sean Paul <seanpaul at chromium.org>
> Cc: <stable at vger.kernel.org> # v4.11+
> Reviewed-by: Dave Airlie <airlied at gmail.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> Link:
> https://patchwork.freedesktop.org/patch/msgid/20171204204818.24745-1-daniel.vetter@ffwll.ch
>
> diff --git a/drivers/gpu/drm/drm_connector.c
> b/drivers/gpu/drm/drm_connector.c
> index 25f4b2e..4820141 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -152,6 +152,16 @@ static void drm_connector_free(struct kref *kref)
> connector->funcs->destroy(connector);
> }
> +static void drm_connector_free_work_fn(struct work_struct *work)
> +{
> + struct drm_connector *connector =
> + container_of(work, struct drm_connector, free_work);
> + struct drm_device *dev = connector->dev;
> +
> + drm_mode_object_unregister(dev, &connector->base);
> + connector->funcs->destroy(connector);
> +}
> +
> /**
> * drm_connector_init - Init a preallocated connector
> * @dev: DRM device
> @@ -181,6 +191,8 @@ int drm_connector_init(struct drm_device *dev,
> if (ret)
> return ret;
> + INIT_WORK(&connector->free_work, drm_connector_free_work_fn);
> +
> connector->base.properties = &connector->properties;
> connector->dev = dev;
> connector->funcs = funcs;
> @@ -529,6 +541,18 @@ void drm_connector_list_iter_begin(struct drm_device
> *dev,
> }
> EXPORT_SYMBOL(drm_connector_list_iter_begin);
> +/*
> + * Extra-safe connector put function that works in any context. Should only
> be
> + * used from the connector_iter functions, where we never really expect to
> + * actually release the connector when dropping our final reference.
> + */
> +static void
> +drm_connector_put_safe(struct drm_connector *conn)
> +{
> + if (refcount_dec_and_test(&conn->base.refcount.refcount))
> + schedule_work(&conn->free_work);
> +}
> +
> /**
> * drm_connector_list_iter_next - return next connector
> * @iter: connectr_list iterator
> @@ -561,7 +585,7 @@ drm_connector_list_iter_next(struct
> drm_connector_list_iter *iter)
> spin_unlock_irqrestore(&config->connector_list_lock, flags);
> if (old_conn)
> - drm_connector_put(old_conn);
> + drm_connector_put_safe(old_conn);
> return iter->conn;
> }
> @@ -580,7 +604,7 @@ void drm_connector_list_iter_end(struct
> drm_connector_list_iter *iter)
> {
> iter->dev = NULL;
> if (iter->conn)
> - drm_connector_put(iter->conn);
> + drm_connector_put_safe(iter->conn);
> lock_release(&connector_list_iter_dep_map, 0, _RET_IP_);
> }
> EXPORT_SYMBOL(drm_connector_list_iter_end);
> diff --git a/drivers/gpu/drm/drm_mode_config.c
> b/drivers/gpu/drm/drm_mode_config.c
> index cda8bfa..cc78b3d 100644
> --- a/drivers/gpu/drm/drm_mode_config.c
> +++ b/drivers/gpu/drm/drm_mode_config.c
> @@ -431,6 +431,8 @@ void drm_mode_config_cleanup(struct drm_device *dev)
> drm_connector_put(connector);
> }
> drm_connector_list_iter_end(&conn_iter);
> + /* connector_iter drops references in a work item. */
> + flush_scheduled_work();
> if (WARN_ON(!list_empty(&dev->mode_config.connector_list))) {
> drm_connector_list_iter_begin(dev, &conn_iter);
> drm_for_each_connector_iter(connector, &conn_iter)
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index df9807a..a4649c5 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -916,6 +916,14 @@ struct drm_connector {
> uint8_t num_h_tile, num_v_tile;
> uint8_t tile_h_loc, tile_v_loc;
> uint16_t tile_h_size, tile_v_size;
> +
> + /**
> + * @free_work:
> + *
> + * Work used only by &drm_connector_iter to be able to clean up a
> + * connector from any context.
> + */
> + struct work_struct free_work;
> };
> #define obj_to_connector(x) container_of(x, struct drm_connector, base)
> -------------------------------------------------------------------------------
>
>
> Git bisection log:
>
> -------------------------------------------------------------------------------
> git bisect start
> # good: [c6b3e9693f8a32ba3b07e2f2723886ea2aff4e94] Merge branch 'for-linus'
> of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux
> git bisect good c6b3e9693f8a32ba3b07e2f2723886ea2aff4e94
> # bad: [50c4c4e268a2d7a3e58ebb698ac74da0de40ae36] Linux 4.15-rc3
> git bisect bad 50c4c4e268a2d7a3e58ebb698ac74da0de40ae36
> # bad: [e9ef1fe312b533592e39cddc1327463c30b0ed8d] Merge
> git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
> git bisect bad e9ef1fe312b533592e39cddc1327463c30b0ed8d
> # bad: [77071bc6c472bb0b36818f3e9595114cdf98c86d] Merge tag 'media/v4.15-2'
> of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media
> git bisect bad 77071bc6c472bb0b36818f3e9595114cdf98c86d
> # bad: [4066aa72f9f2886105c6f747d7f9bd4f14f53c12] Merge tag
> 'drm-fixes-for-v4.15-rc3' of git://people.freedesktop.org/~airlied/linux
> git bisect bad 4066aa72f9f2886105c6f747d7f9bd4f14f53c12
> # bad: [96980844bb4b74d2e7ce93d907670658e39a3992] Merge tag
> 'drm-intel-fixes-2017-12-07' of git://anongit.freedesktop.org/drm/drm-intel
> into drm-fixes
> git bisect bad 96980844bb4b74d2e7ce93d907670658e39a3992
> # bad: [120a264f9c2782682027d931d83dcbd22e01da80] drm/exynos: gem: Drop
> NONCONTIG flag for buffers allocated without IOMMU
> git bisect bad 120a264f9c2782682027d931d83dcbd22e01da80
> # good: [2bf257d662509553ae226239e7dc1c3d00636ca6] drm/ttm: roundup the
> shrink request to prevent skip huge pool
> git bisect good 2bf257d662509553ae226239e7dc1c3d00636ca6
> # good: [db8f884ca7fe6af64d443d1510464efe23826131] Merge branch
> 'drm-fixes-4.15' of git://people.freedesktop.org/~agd5f/linux into drm-fixes
> git bisect good db8f884ca7fe6af64d443d1510464efe23826131
> # bad: [bd3a3a2e92624942a143e485c83e641b2492d828] Merge tag
> 'drm-misc-fixes-2017-12-06' of git://anongit.freedesktop.org/drm/drm-misc
> into drm-fixes
> git bisect bad bd3a3a2e92624942a143e485c83e641b2492d828
> # bad: [a703c55004e1c5076d57e43771b3e11117796ea0] drm: safely free
> connectors from connector_iter
> git bisect bad a703c55004e1c5076d57e43771b3e11117796ea0
> # first bad commit: [a703c55004e1c5076d57e43771b3e11117796ea0] drm: safely
> free connectors from connector_iter
> -------------------------------------------------------------------------------
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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